MS54 - Crystallography at conditions of Earth and planetary interiors

The field of high-pressure crystallography, and in particular, crystallography of planetary interiors, has seen some major discoveries and methodological developments in the last couple of years. Our symposium has focused on these new fields. Different approaches - experimental (static and shock compression) and theoretical - have been covered in talks within this session. The only theoretical talk, given by Colin W. Glass (ETH Zurich, Switzerland), presented a new theoretical methodology allowing one to predict crystal structure of a material at any pressure-temperature conditions from the knowledge of the chemical composition alone. This novel methodology involved state-of-the-art quantum-mechanical calculations and is likely to play a major role in future high-pressure research and materials design. Agnes Dewaele (CEA, France) has addressed a long-standing problem of precise pressure calibration in static experiments. Her new calibration of the ruby pressure scale, based on high-precision experiments, has been confirmed by other independent studies. Thomas Duffy (Princeton University, USA) showed his group's recent results on the high-pressure behaviour of the recently discovered post-perovskite phase of MgSiO3. This major Earth-forming phase, discovered only in 2004, has attracted attention of many research groups worldwide - including the group at Princeton, where many geophysically important results have been obtained. Takehiko Yagi (University of Tokyo, Japan) reported recent experimental results of his team on high-pressure behaviour of FeO, a material that has long posed numerous questions concerning its atomic, electronic and magnetic structure at high pressure. In spite of the simple chemical composition, this material continues to frustrate experimental and theoretical efforts to understand its behaviour on compression. Sheng-Nian Luo (Los Alamos National Lab., USA) has discussed superheating and melting in shock-wave experiments, using phenomenological models, computer simulations and experimental data. On top of the diversity of the talks presented and problems addressed, one thing came through very clearly - that the field of high-pressure mineralogy is only in its start, an
exciting phase for new researchers with new ideas and approaches to enter the quest for understanding the Earth's materials.